Two recent mortality studies have produced evidence that exercise  even light activity such as vacuuming or walking the dog  is healthier than previously believed.

The studies are among the first wave of epidemiological papers based on objective measures of physical activity, rather than self-reported responses, so they are considered more accurate.

The new investigations were performed by researchers at Harvard University and the renowned Karolinska Institute in Stockholm. They found the most active subjects had a 50 percent to 70 percent decline in mortality during a defined follow-up period compared with the least active participants. Previous self-report research had pegged this benefit at about 20 to 35 percent.

We were somewhat surprised by the strong association between light activity and mortality, said Ing-Mari Dohrn, first author of the Swedish paper. It was a strong factor for reductions in cancer and cardiovascular deaths, as well as for all-cause mortality.

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Francisco Lopez-Jimenez, who is not connected to the new research, said the protective benefit of physical activity is larger than we had thought. Lopez-Jimenez is chairman of the division of preventive cardiology and a research director at the Mayo Clinic in Rochester, Minn.

Diet and exercise studies have long been troubled by reliance on self-reporting. Asked how much they eat or exercise, respondents generally under-report their consumption and over-report their exercise.

However, wearable accelerometers like Fitbit have improved the situation for exercise epidemiologists. These allow scientists to collect objective activity data  such as how much they sit, how much they move  on large numbers of people.

I-Min Lee and her Harvard colleagues mailed accelerometers to more than 16,000 U.S. women, who wore them for 15 hours a day on four or more days. The researchers followed the women for an average of 2.3 years to determine their mortality data. The Swedes gave similar devices to 851 subjects, including almost 400 men, who wore them for 14 or more hours on four or more days. These subjects were tracked for 14.2 years.

In other words, one trial observed a large number of subjects, while the other monitored its subjects for many years. Although differing slightly on some methods and outcomes, both studies concluded that subjects who moved a lot enjoyed a substantial longevity benefit over those who moved little.

In addition, the Swedish team found that individuals who sit fewer than six hours a day have a 66 percent lower mortality risk than those who sit more than 10 hours a day.

The different populations in different countries reported remarkably similar measurements for time sitting, light activity (i.e., folding laundry, walking slowly, etc.), and time in moderate-to-vigorous activity (vacuuming, walking briskly or playing sports). It appears both Americans and Swedes spend an average of about 500 minutes a day sitting, 350 minutes in light activity and 30 minutes in moderate to vigorous activity.

The message should remain, as it has been, that 30 minutes or more of moderate-to-vigorous activity daily can reduce risk of (premature) death by 50 percent, Dohrn said.

The studies tracked individuals in their late 60s to early 70s, but both research teams believe the basic results would hold true for people decades younger. Both studies showed that all physical activity counts toward improving health. You dont have to play basketball or run  you simply have to move your body forward, upward or side to side, as when washing windows.

Both papers tracked mortality first, because that yields a simple yes/no outcome measure. However, both teams are investigating other outcomes and believe their findings will apply to chronic-disease illnesses, such as obesity, diabetes and high blood pressure. According to some reports, the economic cost of obesity in the United States is approaching $200 billion per year.